A puncture instrument includes a needle assembly, a hub passage for axially guiding a hub, a needle passage communicating with the hub passage and having a distal end opening for allowing the tip end of a needle to project instantaneously therethrough, two arms having first junctions connected to the hub and inclined rearward in a direction away from the hub in an initial state, two push rods connected to second junctions of the arms and extending rearward, a button for pushing the push rods forwardly, and fulcrum members disposed more closely to the distal end than the arms for abutment against portions of the arms when the arms are moved. When the push rods are pushed forwardly by the button, the arms push the needle assembly forwardly, thereafter have portions thereof brought into abutment against the fulcrum members, and turn to pull the needle assembly rearward.